Poisonous Hydrogen Sulphide Gas

I keep an aquarium as a hobby, and while cleaning a test tube I suspect I may have accidentally created poisonous hydrogen sulfide gas. Here is the situation: I had a glass test tube that was used about 6 years ago to do nitrate tests on saltwater using a Tetratest Saltwater Nitrate test kit. It was then neglected for about 6 years in storage presumably with some of the test solution intact which may have spilled out or evaporated leaving a layer of gray solid on the bottom, most likely zinc (which was part of the test), but perhaps more than just zinc. I had recalled a demonstration where a zinc penny was dissolved in sulfuric acid, so it occurred to me that I could clean this test tube with some 9.6% sulphuric acid that I had as a pH adjuster for the aquarium. I added the sulphuric acid and observed the zinc layer evolving gas, which I believed to be hydrogen, and at this time there was no odor observed. After several minutes I dumped the contents of the test tube into a sink with running water, at this time I smelled a strong rotten egg sulphur odor which I immediately ran away from and once I stopped I felt dizzy. I immediately left the room and looked up sulphur gas on the internet and found out about toxic hydrogen sulphide gas! I felt dizzy for several hours afterwards, and I thought I was going to die. I thought the reaction I was performing was zinc plus sulphuric acid yields hydrogen gas and aqueous zinc sulphate. According to my research zinc sulphate has no odor so I can't attribute the sulphur smell to it. I imagine there could have been more going on in that test tube than I realized. My question: is it possible that I actually made hydrogen sulphide gas, and if so in any significant quantity to harm myself? I feel foolish for being so careless, and I think I'm alright, but I'd like to understand what happened. I have a minor background in chemistry from my college days, but I am very far from being a chemist! I could use some help to understand this and thank you for your time.

It occurred to me afterwards that the solid in the test tube may have been precipitate created from the evaporation of aquarium salt water mix, plus whatever chemicals the nitrate test used in addition to zinc, as well as any compounds contributed by aquarium life (nitrogenous waste, etc.). Assuming that it was only zinc was foolish and may have been a catastrophic mistake. Also, what is the proper procedure to clean a test tube with unknown contents? Perhaps disposal would have been the proper move.

It sounds as if this reaction generated a small amount of hydrogen sulfide gas. Zinc is a reducing agent, and something in the test mixture reacted with it to form zinc sulfide. Addition of acid would release H2S.

The human nose is extremely sensitive to H2S (at the low ppm level) and any level that you can smell is HARMLESS. Higher levels anaesthetize the nose and prevent detection. The symptoms you describe are those of a panic attack. Every chemist knows about the possible chemical hazards and may panic if they think they have been exposed to something dangerous. I've experienced this reaction myself.

Thank you for your response. I'm sure you're right that panicking contributed to my symptoms, but now 13 hours later I'm still getting dizzy when I simply walk around the house. Do you think I need to seek medical attention, or am I just overreacting? I read that you can smell H2S at 0.5 ppm and that after two minutes at 100 ppm you can't smell it anymore. Apparently it's harmful at 20 ppm. I only smelled it briefly and then left the basement where it was, have not smelled it since. I'm assuming that there was not enough generated to reach dangerous levels in the rest of my house, am I right? It was only a few ml of 9.6% sulphuric acid in the test tube, and we're talking about a 1700 square foot house plus a full basement. Is there any way that a few mls of sulphuric acid could generate enough H2S to reach harmful levels in that much air volume? Also I imagine I could have received a larger dose directly at the source. Thank you for your time.

Nos, unless you're experiencing other symptoms (e.g. actual difficulty breathing, nasal or eye irritation, etc.) I think you can stop worrying. It's hard to compare your exposure to the examples listed above, because they all assume chronic exposure as opposed to exposure for a second or two.

The limiting reagent in the reaction would have been the sulfide salt. If the test tube contained 100 mg of pure ZnS, that would be about 1 mmol (or about 24 mL of gas at room temperature). The actual amount was probably less. By the time it's dispersed in a cubic meter of air, the concentration would be 24 ppm or less. Unless you have asthma already, a brief exposure at that level would be insignificant. I hope this response is helpful.

Thank you for your response, that is very reassuring. I'm still feeling sick, but at this point I believe that it is just a coincidence that I have fallen ill. Apparently my niece, who was not exposed to H2S, has also been sick recently.

I thought this was resolved, but unfortunately, I'm affraid that my illness is not something contagious from my niece, but actually the result of exposure to some toxin. I have subsequently concluded, following further research and help from members of this board, that Hydrogen Sulfide, while detected by my nose, did probably not do me significant lasting harm. Considering that I am continuing to have symptoms days later I am considering exposure to other toxins. I have been having bouts of dizziness and fatigue usually following mild physical activity, such as getting up from a chair or climbing stairs; I had these same symptoms, although more intense and persistent, in the minutes and hours immediately following exposure. I am a rather healthy man in my early 30s so such physical activity shouldn't result in such symptoms. I believe that the nitrate test in question is what is known as a Griess test; this test uses an acid solution of sulfanilic acid and alpha-naphthylamine which undergoes a diazotization reaction with nitrites forming a red azo dye. Zinc is added to the test to convert nitrates to nitrites so they can be detected by the Griess test. The question I now have is... When I added sulphuric acid to the dried up remnants of the Griess test in that test tube, what toxic gasses could have been created?

I believe that what you have done is acidify the biological environment in the drain itself, thereby releasing whatever stores of sulfur and other things that were there. Probably not a very fast release of hydrogen sulfide, but it would continue for as long as the pH remained low and was not otherwise flushed away.